A variety of paper sorting machines exists for receiving and sorting sheets of paper from an output slot of, for example, a document copier. Such sheet sorters are of a fixed tray or a movable tray type. With the fixed tray type, all the trays are separated by a fixed and relatively large distance from one another and a movable paper chute delivers the document to a selected tray or to the trays in sequence. Due to the large separation between trays, the fixed tray sorters are large.
The movable tray type sorter is more compact than the fixed tray type. The movable tray type sorter has a set of trays which is arranged in a compact stack with very little separation between the trays of the stack. In such sorters, the trays are moved past a fixed position at which the paper chute is secured. As each tray moves to the position of the paper chute, the separation between the tray at the paper chute position and the next adjacent tray increases to permit movement of a sheet of paper into the selected tray.
A plethora of problems plague sorters of the movable tray type. These problems relate to the movement of the trays where the capacity of the sorter depends on how physically robust the mechanical structure of the sorter is made. But the more robust the mechanical structure, the slower the operation and the more expensive the machine. One patent which addresses this problem is U.S. Pat. No. 4,343,462 issued to Lawrence on Aug. 10, 1982. The sorter disclosed in that patent employs two rotating cam shafts operative to move the trays sequentially past a paper chute in a fixed position. The Lawrence patent is representative of a large number of patents directed to the issue of paper tray movement.
Other problems relating to movable bin or tray type sorters involve the placement and retention of multiple sheets of paper in the trays, the speed of tray movement, and the simplification of the tray selection and movement control to provide a reliable and yet inexpensive paper sorter.
These problems are more acute in sorters where the trays are oriented in an almost vertical orientation rather in a stack of horizontally oriented trays. The relative lack of commercial success of sorters with vertically oriented trays is testimony to the failure to successfully resolve some of the outstanding problems with such sorters.